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Colin R. Parrish, Ph.D.

John M. Olin Professor of Virology

Dr. Colin Parrish’s research focuses on certain viruses of dogs, cats, and horses that still cause a significant number of illnesses and deaths despite the availability of effective vaccines. Each of these viruses also has a history of moving from one species of animal into another and causing an epidemic, and Dr. Parrish’s lab is working on understanding the principles behind how this emergence in new hosts works. Dr. Parrish’s current projects explore the evolution of canine parvovirus, ways to predict outbreaks of new and old viruses, and approaches that may be used for eradicating canine influenza, all efforts with the potential for a significant impact on the health of dogs, cats, horses, and wildlife. An animal lover, Dr. Parrish and his family share their home with five cats and three dogs.

Canine parvovirus first appeared in 1978 in a global pandemic that killed dogs by the hundreds of thousands. Although it evolved from feline panleukopenia virus, which is specific to cats, canine parvovirus now appears to infect most carnivores worldwide (members of the Order Carnivora), including carnivores native to North America, many of which are critically endangered. Genetic evidence indicates it all started when a single feline panleukopenia virus mutated and gained the ability to attach to receptors on the cells of dogs. Dr. Parrish and his colleagues are studying how the virus has evolved since 1978, tracking the spread of new variants of the virus and the ways they differ from their predecessors. This natural variation in the virus over time could make problems for vaccination efforts, so they’re also taking a close look at the structure of the viral surface and how the virus attaches to host antibodies and to the receptors on the surface of dog cells. This will allow them to determine whether the vaccine for parvovirus is still a good match for the strains that are in circulation, and if the vaccine and the virus are mismatched, it may be time to update the parvovirus vaccine.

On a related vein, Dr. Parrish’s laboratory is using molecular information like this to predict and to prevent the emergence of new epidemics of viral disease. Zoonoses are diseases that jump from animals to human populations (like the pandemic influenza strain of 1918, Ebola, and rabies). Zoonotic diseases are becoming increasingly common, most likely as a result of increasing intensification of agriculture and human encroachment on wild areas, and their ability to cross international borders easily makes them a global problem. Working with an international team of scientists, Dr. Parrish’s lab is studying the properties of host-jumping animal viruses and receptors on host cells and putting this information into the context of human and animal exposure to viruses, transmission, global travel, and other factors, in an attempt to understand the fundamental principles behind the emergence of new diseases. By weaving all this information together into a mathematical model, it may also be possible to identify viruses in animals that might someday cross over to humans, allowing public health authorities to put interventions in place to stop that from happening.

Influenza is one virus that’s particularly well-known for crossing between different species. Dr. Parrish’s lab is studying H3N8, a flu strain that jumped from horses into dogs in 1999, which lead to a widespread outbreak in the following few years, but today the virus seems to be maintained only in dogs at a handful of large animal shelters. It’s not well understood why, after 14 years of continuous circulation, “dog flu” hasn’t spread widely among the general dog population. Dr. Parrish and his colleagues are studying the genomes of the virus and modeling the rate at which it moves from dog to dog to determine why H3N8 has died out in many locations and how control measures might be used to further limit spread. Their early results show the virus is not very transmissible, and that to maintain disease in a population each infected dog would have to have contact with two or three other dogs during the short period when the animal sheds significant numbers of viruses. These results indicate that control measures should be possible to eradicate “dog flu”, an accomplishment that would represent a rare achievement in animal health.